Hard disk drives (HDDs) using rotating media are a low-cost and robust solution for permanent storage of data. Current generations of HDDs exist in different form factors, with the 2.5″ form factor prevailing in the mobile sector and the 3.5″ form factor being the most common solution in desktop, server and workstation environments. The system interface of either of the above form factors may conform to the Serial Advanced Technology Attachment (SATA or Serial ATA) or the Serial Attached Small Computer System Interface (SAS), standard with the first being prevalent in the consumer market segment and the latter more commonly used in the enterprise market segment.
Contemporary high density storage servers are typically modular designs having a drive enclosure and provisions to plug in additional modules into a server or storage bay. The modules are typically server modules that connect to the outside world through Ethernet or Fibre Channel (FC) or else Input/Output (I/O) modules that interface with the outside world through SAS connections. The modules are also typically field-replaceable units (FRUs), whereas the drive enclosure is the main unit of the entire configuration and uses a base board (also referred to as base plane or drive plane) as an interface to the drives. The drives are inserted from the top of the enclosure, which is referred to as a top-loading configuration. Hard disk drives are using industry standard form factors, for example, the currently prevalent 3.5″ drives are generally referred to as large form factor drives with standardized outside dimensions. Server enclosures are generally standardized with respect to their dimensions as well, therefore, any increase in the number of drives in the available space will result in the cannibalization or reduction of the space in between the drives with the caveat that that particular space serves as plenum for cooling fluids. Accordingly, increasing the number of drives in the enclosure will reduce the amount of cooling fluid available. In the majority of cases, the cooling fluid will be air.
Data centers are laid out in a way that rows of servers have their front end in an area receiving cold air from air conditioning units. The cold air is taken in by the servers and warms up when passing through the electronics. The hot air is expelled into an area that exhausts the hot air. The intake and exhaust areas of the data centers are generally referred to as hot and cold isles, respectively.
Turning to FIG. 1, a typical server enclosure 100 as used in most current designs is illustrated. The enclosure 100 has four different compartments, the first compartment 110 contains the actual server module having a motherboard 111, a microprocessor 112, memory modules 113 and input output (I/O) ports 115. A high density connector 114 connects the motherboard to a drive carrier board 121, located inside the drive bay 120. The drive carrier board 121 contains drive connectors 125 which may be a small form factor (SFF) 8639 (U2) or any other suitable form factor known in the art and into which the drives 123 are plugged.
The system power supply 131 is located in the power supply bay 130 and has an exhaust fan 136 to expel hot air into the hot isle. The coolant or air 150 is drawn in from the cold isle by an array of fans 146 located in a system fan bay 140 and gradually warms up while passing between the HDDs over the different components inside the server enclosure 100. For an array of drives with each drive dissipating heat, that means that the drives located further away from the cold air intake will be subjected to increasingly pre-warmed air which greatly reduces the cooling efficiency. Increasing the number of drives in the system at the expense of the available air gap will exacerbate the situation.
In view of the aforementioned problems relating to maintaining cooling efficiency across increased-density arrays of HDDs in enclosures, it is clear that alternative solutions are necessary.